Is this another example or an ad?

There's a box that looks like an advertisement at the bottom of the Appeal to Extremes page I was referencing.

"Eat Meat... Or Don't.
Roughly 95% of Americans don’t appear to have an ethical problem with animals being killed for food, yet all of us would have a serious problem with humans being killed for food. What does an animal lack that a human has that justifies killing the animal for food but not the human?"

Is this an ad used as an extreme example or an actual advertisement?

An axe?!

It is an ad. The appeal to extremes is "erroneously attempting to make a reasonable argument into an absurd one, by taking the argument to the extremes."

I am guessing you are conflating the absurd hypothetical I referenced (killing humans for food) with the argument being absurd itself. Plus, this doesn't follow the form of the fallacy:

If X is true, then Y must also be true (where Y is the extreme of X).

The fallacious version would go as follows:

"If it's true that eating fish is okay, then it also must be true that eating humans is okay," where "humans" is can be seen as the extreme form of life (in terms of complexity, consciousness, etc.).

As an aside (not that it matters here), in the book, I discuss the actual problems with this argument. The book is NOT a book that supports veganism.